Free-living diazotrophs drive castor bean nitrogen input in tropical semiarid soils

Abstract

There are few studies of microbial diversity in castor bean soils in tropical semiarid environmental. Castor bean products have been widely used around the world justifying the commercial importance of ricinoculture in Brazil’ northeastern semiarid. There is no fertilization or maintenance of litter on the soils from the present study, so we hypothesized that the free-living diazotrophs microorganisms drive the nitrogen (N) input into these soils. We evaluated the communities’ structure and diversity of diazotrophs in tropical semiarid soils with i-Castor bean 50 years of cultivation intercropping with maize (CB-50); ii-Only Castor bean 10 years of cultivation (CB-10) and iii-soil under Caatinga vegetation (CAA). Nitrogenase enzyme activity was performed by the acetylene reduction assay (ARA) and the community profile of nifH gene was separated by denaturing gradient gel polyacrylamide electrophoresis (DGGE). Diazotrophs diversity was estimated by the Shannon (H’) and Simpson (D) indexes. Based on the maintenance of soil N stocks and N-microbial biomass over time, the activity of free-living diazotrophs was determinant in the N-input into these soils. The nifH gene was present and its profiles grouped the CB-50 with CAA treatments, so it reinforced the N-fixing by diazotrophs, which presented a greater diversity in the cultivated soils, even after the land use change for the castor bean implementation.

Selection of green manures to provide ecosystem services in a semi-arid environment

“…Among the single crops, castor bean (T12), an oilseed species with good capacity for extracting nutrients in deep layers (Savy Filho et al, 1999) and producing biomass (Favarato et al, 2017), stood out among other species, including legumes. Studies demonstrate the importance of the diversity and activity of free-living diazotrophs in the entry of N into soils cultivated with castor bean, being important for maintaining nitrogen stocks in the soil and microbial biomass over time (Mendes et al, 2015;Fracetto et al, 2019). In addition, this species showed similar or higher N accumulation capacity than treatments with a greater number of species, including in the root system.…”